This chemoprevention trial tests the efficacy of retinol and beta- carotene in preventing lung cancer in two related high-risk populations: (a) heavy smokers recruited from insurance-based sources, and (b) current and former workers with heavy occupational asbestos exposure recruited from workers' compensation and employment-based sources. The double-blind two-arm randomized protocol compares placebos with a daily combination of 30 mg beta- carotene plus 25,000 IU retinol. We will recruit eligible asbestos-exposed subjects from the San Francisco/Oakland area. We will participate in implementing a cost-effective, well-integrated, multi-clinic strategy, with the Seattle-based coordinating center for project management and data analysis. During the first 3 years of the new grant period (1988-91) we will recruit and enroll 800 subjects randomized according to the multi center protocol. We will provide all necessary data to evaluate accrual, coordination, and costs in geographically-dispersed clinic sites to generate best estimates of the remaining needs for the full-scale enrollment and follow-up. Current assumptions and projections indicate that the full-scale Efficacy Trial will be capable of detecting significant reductions in lung cancer incidence in the high-risk groups combined, and in either subgroup alone, with 13,000 smokers and 4000 asbestos-exposed subjects.